Vacuum gate valves are used to close off an opening in a container or pipeline. Vacuum gate valves primarily of the L-type are utilized in IC and semiconductor manufacturing to exclude, to a large extent in a protected atmosphere, the presence of contaminating particles. For instance, in a production unit for semiconductor wafers or liquid-crystal substrates, the highly sensitive semiconductor or liquid-crystal elements pass through a number of production chambers each of which can be connected to the next via a connecting passage. These passages are opened via vacuum gate valves so that the elements can be transferred from one production chamber to the next and then closed again in gas-tight fashion so that continuing production steps can be performed.
A general schematic of a related art vacuum gate valve is illustrated in FIGS. 1a, 1b and 1c. 
FIG. 1a shows the vacuum gate valve in its opened initial position. The vacuum gate valve can have a valve housing 1 with a wall 2 having an opening 3 (e.g. of rectangular shape). A valve seat 4 formed as a flat surface or a surface of special shape, with or without a seal, surrounds the opening 3. A valve plate 5, which in the opened initial position of the vacuum gate valve is positioned in a lateral position to the opening 3, close to the wall 2, is shown in FIG. 1a. The valve plate 5 has a shape, more particularly rectangular, which overlaps the opening 3 in such a way that the opening can be closed off entirely with a sealing face 7 of the valve plate 5. The valve plate 5 is mounted on a valve rod 8 defining a valve rod axis 11. Instead of one single valve rod 8, two parallel valve rods can be can utilized.
The valve rod 8 can essentially be controlled along two degrees of freedom by control organs 10, for instance by a hydraulic-cylinder and swivel-gear unit, as will subsequently be shown in FIGS. 1b and 1c. More particularly the valve rode 8 can be shifted linearly along the valve rod axis 11 and swivelled in a plane normal to wall 2.
In related art systems, closing off the opening 3 is done in two steps. In a first step, occurring between the situations shown in FIGS. 1a and 1b, the valve rod 8 is extended by means of the control organs 10 along the valve rod axis 11, which is shown by two arrows 28a and 28b. The valve plate 5 is moved over the opening 3 along a path essentially parallel to the wall 2 while avoiding contact between the valve plate 5 and the wall 2 or the valve seat 4 of the valve housing 1.
In a second step, occurring between the situations of FIGS. 1b and 1c and symbolically represented by the arrow 28c, the valve rod 8 is swivelled toward the wall 2 by the control organs 10, so that the sealing face 7 of the valve plate 5 (which may for instance hold a sealing ring) is pressed against the valve seat 4 and the opening is closed off firmly, where applicable in a gas-tight fashion. Sealing can be realized, for instance, either via a sealing ring disposed on the sealing face 7 of valve plate 5 and pressed against the valve seat 4 surrounding the opening 3, or via a sealing ring disposed on valve seat 4 against which the sealing face 7 of the valve plate 5 is pressed. The valve seat 4 is generally defined as the opposing face on wall 2 onto which the sealing face 7 of valve plate 5 is pressed, and which thus causes the sealing.
Different sealing devices are known from the related art, for instance from U.S. Pat. No. 6,629,682 B2. The elastic sealing material known under the trade name of Viton®, for instance, is a suitable material for sealing rings. In view of the closing operation occurring in two steps, the sealing ring will hardly be subjected to any shear forces that might destroy it, since the swivelling motion of the valve rod 8 causes an essentially straight-line movement of the valve plate 5 normal to the valve seat 4. From the related art, various kinds of control organs 10 are known which each may give rise to a slightly different direction of control of valve rod 8 and thus of the valve plate 5. Thus, instead of an arched swivel path of valve plate 5 toward valve seat 4, an absolutely linear motion of the valve plate 5 normal to wall 2 can be initiated. Diverse embodiments of vacuum gate valves of the kind cited above are known, for instance, from U.S. Pat. Nos. 6,431,518 B1, 5,415,376 A, 5,641,149 A, 6,045,117 A, 5,934,646 A, 5,755,255 A, 6,082,706, 6,095,180 and 6,629,682 B2.
A particular problem in the related art is the alignment of valve plate 5 relative to valve housing 1. In the first step, moving the valve plate 5 over the opening 3, contact of the sealing face 7 with wall 2 or valve seat 4 can lead to injury to a sealing surface or to the sealing ring. Additionally, in the second step, where pressure is applied, the valve plate 5 should have a precise alignment relative to the valve seat 4, since otherwise the sealing face 7 of the valve plate 5 may not reach its precise position on the valve seat 4.
In related art systems the planes of sealing face 7 and valve seat 4 should be parallel while the pressure is applied, since otherwise the sealing surface along the valve seat would be stressed non-uniformly, which could give rise to poor tightness and to a degradation of the sealing material. Moreover, the valve plate 5 and the valve rod 8 would be subjected to bending and torsional forces. For this reason, control organs 10 in the related art attempt to precisely align the valve rod 8, and thus the valve plate 5.
The joint between valve rod 8 and valve plate 5 is formed for instance by means of a connecting segment 9 on valve rod 8 which is guided into and fastened inside a receptacle 6 formed in valve plate 5. The fastening occurs for instance as described in U.S. Pat. Nos. 6,068,180 and 6,619,618, namely by means of at least one screw inserted from the side opposite to the sealing face.
U.S. Pat. No. 6,619,618 illustrates a vacuum gate valve which has a valve plate of non-uniform wall thickness, viz., thicker in the middle than in the two lateral zones. In the central, thick-walled zone, a semicircular receptacle for a valve rod is formed, the wall thickness between the receptacle and the sealing face being large relative to the wall thickness between the receptacle and the face opposite to the sealing face. The valve rod, at its end, has a connecting segment which also is semicircular, and is introduced into the receptacle. The valve plate is solidly mounted onto the valve rod by means of a screw, screwed in from the side opposite to the sealing face. With the design of valve plate, receptacle and connecting segment, as described in U.S. Pat. No. 6,619,618, it is intended to avoid excessive bending of the valve plate when pressed onto the valve seat, particularly in the lateral zones of an elongated valve plate, without the need for more than a single shaft or larger overall thickness of the valve plate.
In related art systems, the valve plate 5 is subjected to controls or maintenance at certain time intervals, particularly for checking or replacing the sealing ring, in order to attempt to increase the lasting tightness of the vacuum gate valve. With the vacuum gate valves known from the related art, the demounting and re-mounting of the valve plate is found to be difficult, since an intervention from several sides of the valve plate is required to detach the valve plate from the valve rod, e.g. in order to unfasten any mounting screw and take off the valve plate from the valve rod. A safe demounting is not readily achieved without injury to the valve plate 5 or valve housing 1, and particularly the valve seat 4, because of poor ergonomic possibilities for handling the valve plate.